<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8"/>
        <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
        <meta http-equiv="X-UA-Compatible" content="ie=edge"/>
        <title>Document</title>
        <style>
            #small{width: 300px; height: 560px; position: absolute; left: 100px; top: 100px}
            #small img{width: 100%; height: 100%}
            #mark{display: none;width: 200px; height: 200px;  background-color: white; opacity: 0.5; filter: alpha(opacity=50); position: absolute; left: 0px; top: 0px}
            #big{display: none;width: 400px; height: 400px; border: 1px solid black; left: 500px; top: 100px; position: absolute; overflow: hidden;}
            #big img{width: 600px; height: 1120px; position: absolute; left: 0px; top: 0px}
        </style>
        <script>
            window.onload = function(){
                var oSmall = document.getElementById("small");
                var oBig = document.getElementById("big");
                var oMark = document.getElementById("mark");
                var oBigImg = oBig.getElementsByTagName("img")[0];

                oSmall.onmouseover = function(){
                    oMark.style.display = 'block';
                    oBig.style.display = 'block';
                }
                oSmall.onmouseout = function(){
                    oMark.style.display = 'none';
                    oBig.style.display = "none";
                }

                oSmall.onmousemove = function(ev){
                    var e = ev || window.event;
                    var l = e.clientX - oSmall.offsetLeft - 100;
                    var t = e.clientY - oSmall.offsetTop - 100;
                    if(l <= 0){
                        l = 0;
                    }
                    if(l >= 100){
                        l = 100;
                    }
                    if(t <= 0){
                        t = 0;
                    }
                    if(t >= 360){
                        t = 360;
                    }
                    oMark.style.left = l + 'px';
                    oMark.style.top = t + 'px';

                    /* 
                        右边图片的移动方式，左边遮罩层如何移动，右边图片，反方向对应倍数移动
                    */
                    oBigImg.style.left = l * -2 + 'px';
                    oBigImg.style.top = t * -2 + 'px';
                }
            }
        </script>
    </head>
    <body>
        <div id = 'small'>
            <img src="timg.jpeg" alt=""/>
            <div id = 'mark'></div>
        </div>
        <div id = 'big'>
             <img src="timg.jpeg" alt=""/>
        </div>
    </body>
</html>